Several RF systems containing power amplifiers are characterized in recurrent periods of signals having large peak excursions, which should be handled, in order to improve the efficiency of these systems. One way to handle signals with large peak-to-average ratios is to control the DC power supply to a power amplifier. One voltage level is supplied to such a power amplifier whenever the instantaneous amplitude is below a given level (normal operating condition), and an enhanced (and higher) voltage level whenever the instantaneous amplitude is above said level. This solution is described for example, in WO 01/67598, which discloses circuitry for dynamically enhancing the operating voltage of an RF amplifier. However, efficiency of the voltage enhancement circuit disclosed therein may be further increased by controlling the impedance values at the connection point between the power amplifier and the power supply, during normal operation and during voltage enhancement time periods.
It is therefore desired to allow a power amplifier to work under different operating power supply voltages, in response to different input signals or conditions under which the power amplifier, or a component contained within it, operates. For example, in order to optimize the operation of a power amplifier, it has been found beneficial to provide it with a DC power through a first supply path whenever the signal at its input is below a predetermined level, and add a second and a third supplemental power supply paths at instants wherein the signal at its input is above that level, thus enhancing the effective voltage supplied to said power amplifier. This type of solution allows operating a power amplifier in a relatively large dynamic range with high efficiency, as the enhanced operating voltage source is coupled to the circuit only when required by the large instantaneous amplitude.
U.S. Pat. No. 6,831,519B2 discloses circuitry that allows efficient enhancement of the voltage supplied to a power amplifier during required time periods. This circuitry controls the level of the voltage supplied to a power amplifier, via a supplementary supply path that is connected to the feeding point, during both the enhancement period, and periods of normal operation (also called “normal period”). However, the level of enhancement provided by the circuitry of has not been sufficient for more high power applications. In addition, in the circuit of U.S. Pat. No. 6,831,519 the enhancement current is provided by a coupling capacitor, which has a limited capability to pass low frequency components of the enhancement pulse.
It is therefore an object of the present invention to provide improved circuitry that allows efficient enhancement of the voltage supplied to a power amplifier during enhancement periods, while minimizing envelop distortion of the amplified RF signals.
It is another object of the present invention to provide improved circuitry for efficiently controlling the level of the voltage supplied to a power amplifier, via two supplementary supply paths that are connected to the feeding point, during both the enhancement period, and periods of normal operation.
It is another object of the present invention to provide improved circuitry for efficiently controlling the impedance at that feeding point in the direction of the power amplifier and of the supplementary supply path, during both the enhancement period, and the normal period.
Other objects and advantages of the invention will become apparent as the description proceeds.